In a reproducing device for a motion picture film, a CCD (charge-coupled device) line sensor reads out a tracking pattern recorded on the motion picture film for carrying out tracking and reads out a dot pattern of audio data to produce a time varying signal (also referred to herein interchangeably as an "RF signal" or signals). The RF signals are sliced by a comparator at a certain level and the resulting waveform is converted into digital data with the slicing level as reference. Since the slicing level is crucial in converting an analog signal to a digital signal, it needs to be set at a correct and proper position. Therefore, a reproducing device for a motion picture film sets the reference level for the RF signals at a proper value for adjusting the RF signal level for setting the slicing level at an optimum level.
In certain AGC circuits, the amplitude of a Rf data portion is adjusted to a prescribed value, and the slicing level is set to an optimum level with a film on which a dot pattern of a prescribed concentration level is recorded, for example, a level of crossing with an eye pattern of an audio data part.
However, in actual motion picture films, the level of an eye pattern crossing differs with variations in the concentration of a dot pattern recorded on a negative or positive film, even if the RF data portion is of the same amplitude. Therefore, it is difficult with this AGC circuit to set the slicing level at an optimum position.
In other AGC circuits, the average level of the audio data part of the Rf signals is set as the prescribed level. This AGC circuit is superior to the above-mentioned AGC circuit since the crossing level of the average level of the audio data part of the RF signals and the eye pattern varies similarly to changes in the film concentration.
However, if the proportions of the high level portion or the low level portion of the audio data part are offset to one side, the average level of the RF signals is changed under such effect, thus again leading to unstable slice level setting.
In still other AGC circuits, the level of the tracking pattern portion of the RF signals during correct tracking is set as a prescribed level. In these AGC circuits, the level of the tracking pattern portion in the RF signals and the eye pattern crossing point are substantially the same and are varied similarly to the changes in the film concentration. Thus, if the level of the tracking pattern portion is controlled to be a prescribed level, the RF signals can be sliced extremely stably.
However, the pattern recorded on a film is varied in its position along the film width. This variation is produced due to variations in the film running position along its width during pattern recording or to position deviation of the negative or positive film during printing.
Also, during reproductions, the film running position is fluctuated along its width on the running system, so that the reproducing timing of the RF signals fluctuates on a CCD output. Since the audio data portion has a wide pattern width, data sample pulses generated from the CCD start timing are not deviated in the pulse positions from the data area.
However, since the tracking pattern portion is of a narrow width as compared to the amount of change in the signal position, no sampling pulse can be produced from the fixed timing. Thus, the sampling pulses need to be generated from no other than the timing of the playback RF signals.
However, since the level of the tracking pattern portion is detected in a shorter time, it becomes necessary to detect the sampling pulses from a leading position of data from the RF signals for detecting the level for producing the sample pulses.
Moreover, if the RF signal level is deviated significantly from the prescribed value under prevailing conditions of the motion picture film or the light source, the data leading position cannot be detected correctly, such that proper sampling pulses cannot be produced and hence the AGC cannot be operated. In view of the above-described status of the art, it is an object of the present invention to provide a motion picture film reproducing apparatus whereby the prescribed level can be set to an optimum level for the RF signals and the RF signal gain can be controlled for proper digital conversion of RF signals.